Hi, Amani. Go to "themes" and then just click on the theme you want. It's really that simple.
Oh, yeah - the theme should be saved in the \wp-content\themes folder. Good luck! Cheers, Carl Weaver Carl Weaver Photographer http://www.carlweaver.com http://www.camerasamurai.com http://www.dcmetrostories.com - Stories about the people, places and events in the DC Metro Area http://nextlifeintheafternoon.com - A Journey Through Thailand